Several options exist that allow users to send faxes beyond the traditional direct connection between two fax machines across the public switched telephone network (PSTN). One such method is an e-mail fax. Some service providers allow users to send faxes to recipient's e-mail addresses as attachments. Typically, recipients in these types of service must be registered users of the service.
An alternative method of email fax is to map fax numbers to recipient's e-mail addresses. When that number is dialed, the system determines to what e-mail address that number has been mapped and then e-mails the images to the appropriate address. In this type of system, each sender must have an address book installed on the sending system and the recipient must reside at a known e-mail address listed in the book.
Another option for non-traditional fax transmission is fax forwarding. In fax forwarding, a message from the sender is moved across the Internet and to the recipient's area code. This service requires that the fax forwarding service have a switch in the recipient's PSTN area code. A drawback is that the faxes are not real-time.
Fax pirating involves bundling fax messages and then storing them. The faxes are sent during off-peak times. This option does not allow real-time transmission, but can be helpful in countries where there are limited phone resources.
An emerging area that offers non-traditional fax transmission is Internet ready telephones. These may be known as Web phones. Two different options serve as examples of possibilities that exist with these phones. In a first example, each telephone switch in the PSTN would have a hypertext transmission protocol (http) server and a fixed Internet Protocol (IP) address. When an incoming phone call comes in that is directed to an area code outside the caller's area code, the server looks up the fixed IP address of the switch in the call recipient's area code. The system would then establish a virtual circuit between the two switches over the Internet. At the call recipient's end, the switch would then rout the call to the caller over the PSTN in the local area code. An example of this method is shown in U.S. Pat. No. 6,069,890.
Another option using Web phones or their equivalent is to have the server in the telephone device. Each device would then have a fixed IP address. The two phones connect through the PSTN, exchange the necessary information to establish a network connection and then reconnect through the Internet.
As can be seen by the discussion above, the current state of the art does not provide a method to provide real-time faxes across the network, except as e-mail attachments, without providing fixed IP addresses. Fixed IP addresses are difficult to manage and require extra connection protocols, since most connections are done with dynamic IP address assignments. In addition, these approaches waste IP address protocols, as some of the fixed addresses may be assigned to devices that become inactive, but there is no method to reassign the address.